Dynamic changes in histone modification underlie the transition of gametic chromatin to embryonic chromatin. These changes are thought to be required for initiation of embryonic gene transcription and acquisition of pluripotency. Abnormalities in these transitions are likely to result in embryonic arrest at early preimplantation stages. Early embryonic mortality is a major cause of infertility in dairy cattle and humans. In bovine embryos, methylation of histone H3 lysine 27 is one of the epigenetic marks that are dynamically remodeled. Trimethylation of histone H3 lysine 27 is associated with silencing of transcription. We hypothesize that JMJD3, a histone H3 lysine 27 demethylases, is required for removal of methylation marks from H3K27, which in turn allows the initiation of embryonic gene transcription and normal embryo development. To test this hypothesis we will induce downregulation of JMJD3 in bovine oocytes and preimplantation embryos by siRNA injection. Specific Aim 1 will determine whether maternally inherited JMJD3 is required for normal bovine embryonic development. Specific Aim 2 will make use of chromatin immunoprecipitation to assess the role of JMJD3 on histone methylation reprogramming at the time of embryonic genome activation. Specific aim 3 is designed to examine the role of JMJD3 on genome activation by analyzing the transcriptome of early embryos using RNA-seq. Together; these experiments will expand our understanding of the basic mechanisms underlying embryonic development. This information will aid in developing diagnostic tools and interventions to treat infertility disorders in animals and people. Also, uncovering the nuclear reprogramming mechanisms elicited by the oocyte will help improve the success of somatic cell nuclear transfer for the generation of cloned animals for agricultural and biomedical applications and autologous stem cells for regenerative medicine applications.